Apparatus for horizontal fillet welding of steel plates

ABSTRACT

A method and apparatus for horizontal fillet welding of steel plates, particularly coated or painted steel plates, in which two spaced apart welding wires are directed toward the line of intersection of a vertical steel plate and a horizontal steel plate to be welded together so that the centerline defined between the two wires intersects with such line of intersection. The wires are alternately fed toward the line of intersection in such a manner that one of the wires is fed to the vertical plate at a first predetermined rate and the other of the wires is fed to the horizontal plate at a second predetermined rate which is greater than the first rate.

This application is a divisional application of application Ser. No.654,950 filed Feb. 3, 1976, now U.S. Pat. No. 4,058,700.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an arc welding process and apparatusfor preventing the occurrence of pits and blowholes which are oftentimes generated when steel plates coated with, for example, anti-rustpaint, are butted together in a T-shape for horizontal fillet welding,thus obtaining an improved weld bead appearance.

In shipbuilding and bridge construction, a large portion of the weldjoints are fillet welds, so that an automated fillet welding techniquewill improve upon the efficiency of the overall welding operation.

2. Description of the Prior Art

Gas shielded arc welding, submerged arc welding and other weldingtechniques are all capable of being automatically carried out. However,when fillet welding steel plates coated, for example, with anti-rustpaint, the gas generated by the decomposition of the anti-rust paintcauses pits and blowholes in the plates, thus requiring additional laborfor repairs which decreases the efficiency of the operation.

Furthermore, during such horizontal fillet welding the generated arc iscustomarily not made coincident with the line of intersection betweenthe horizontal steel plate and the vertical steel plate, but is insteaddirected at the top surface of the horizontal plate. Such is illustratedin the prior art, as shown in FIG. 1 wherein a vertical steel plate 1 isdisposed in perpendicular fashion to a horizontal steel plate 2 and thefillet welding operation is carried out with the use of a power supplynozzle 3 supporting a welding wire or electrode 4. The center of thegenerated arc is normally off center from the line of intersection ofthe plates by a distance × of approximately 2mm from the vertical plate.The reason for this is that when the arc is directed toward such line ofintersection, an undercut 5 of the weld bead 6 results in vertical steelplate 1, typically as shown in FIG. 2.

Moreover, it has been found that the above-mentioned deviation of thearc center by the distance × likewise causes the anti-rust paint of thehorizontal steel plate to decompose at the butt section of the verticalsteel plate and the horizontal plate, whereby the decomposed gas iscontained within the weld bead, which itself develops pits andblowholes.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to avoid theabove-mentioned drawbacks. An improved welding zone is effected by theinvention by regularly and alternatively feeding during a single passtwo welding wires so as to provide an arc welding process for horizontalfillet welded joints wherein the generation of blowholes is avoided inthe horizontal fillet welding zone.

Another object of the present invention is to provide a horizontalfillet welding apparatus which carries out the above-mentioned arcwelding method effectively.

Other objects, advantages and novel features of the invention willbecome more apparent from the following detailed description of theinvention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end elevational view illustrating a horizontal filletwelding technique in accordance with the prior art.

FIG. 2 is an enlarged sectional view of FIG. 1 illustrating a weld beadand an undercut typically caused by conventional welding techniques.

FIG. 3 is a schematic side view of a welding apparatus according to thepresent invention, shown in relation to the perpendicularly relatedplates of FIG. 1.

FIG. 4 is an enlarged view of the welding section of FIG. 3.

FIG. 5 is an enlarged plan view of a welding wire feed roll takensubstantially along line 5--5 of FIG. 3 used to carry out the method ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus according to the present invention will be described withreference to FIGS. 3 to 5, FIGS. 1 and 2 illustrating the prior art asdescribed above.

Welding electrodes in the form of wires 7 and 8 are unwound from weldingwire feed reels 9 having axes disposed parallel to one another so thatthe unfed wires 7 and 8 are likewise disposed in parallel. The wires areextended to the intended weld zone of plates 1 and 2 through a powersupply nozzle 10, and a wire feed roll 12 driven by a motor 11 isprovided between power supply nozzle 10 and feed reels 9 for carryingout the unwinding operation. The outer peripheral surface of wire feedroll 12 is disposed in contacting engagement with a smooth surface of apressure roll 13 as shown in FIG. 5.

Parallel welding wires 7 and 8, which are spaced apart a distance ofless than about 2mm, are so disposed that the centerline (dotted line inFIG. 4) between them substantially intersects with the line ofintersection between vertical steel plate 1 and horizontal steel plate2, with the end tips of the power supply nozzle 10 being spaced fromsuch line of intersection by about 15 to 25mm (See Fig. 4).

A drive unit 20 is provided for moving nozzle 10 parallel to and alongthe line of intersection defined between vertical steel plate 1 andhorizontal steel plate 2. Such a unit is designed to move nozzle 10 at aconstant speed along the aforedescribed line of the intersection.

Pressure roll 13 is mounted for free rotation about its axis and isrotated solely by the rotation of wire feed roll 12 in rolling contacttherewith.

Parallel grooves 15 and 16 are disposed in the outer peripheral surfaceof wire feed roll 12, which roll is normally rotated at 30 to 80 rpm.Each parallel groove 15,16 comprises a narrow guide groove 17 having across-sectional dimension substantially equal to the diameter of thewelding wire, and a guide groove 18 wider in cross-section than groove17 as shown in FIG. 5. The narrow and wider guide grooves of groove 15are disposed oppositely of the wider and narrow guide grooves of groove16, respectively, so that the narrow and wider guide grooves arepositioned alternately, as shown. At least one narrow guide groove 17and one wider guide groove 18, having their centerlines coincident, openinto one another for each parallel groove 15 and 16, although more thanone narrow and one wider groove for each parallel groove may be providedwithout departing from the invention.

The width of the narrow guide groove 17 in each of the grooves 15 and 16is determined by each diameter of welding wires 7 and 8 to be fed, andthe length of each guide groove 17 is determined by each feed timedesired for welding wires 7 and 8.

Welding wires 7 and 8 are fed by their length corresponding to thelength of narrow guide groove 17 by the frictional force generatedbetween narrow guide groove 17 and pressure roll 13, but they are notfed in wide guide groove 18 because no frictional force is generatedtherein.

The positive side of a welding power unit 19 with a DC constant voltagecharacteristic is connected to power supply nozzle 10, and the negativeside is connected to horizontal plate 2, as in the normal manner.

As mentioned above, the welding operation carried out with the presentapparatus is performed alternately by igniting one welding wire duringits feeding condition for melting same by the arc in the customarymanner, and extinguishing the other welding wire which is in the stoppedcondition for feeding.

The method which is carried out by using such apparatus will bedescribed with reference to FIG. 4.

As shown in FIG. 4, two welding wires 7 and 8 are alternately fed fromthe solid power supply nozzle 10 to the line of intersection betweenvertical steel plate 1 and horizontal steel plate 2, although this isnot the simple alternate feed of two welding wires, but is improvedfurther in the feed conditions thereof.

In the present invention, the respective welding wires for the verticaland horizontal steel plates are of different diameters so as to renderthe welding currents thereby produced different, and/or they are fed atdifferent intervals. In such case, the welding wire for the verticalsteel plate is of a smaller diameter (therefore, the narrow guide grooveis accordingly more narrow), to lower the welding current, and/or thefeed time of the welding wire for the vertical steel plate is madeshorter (therefore, the narrow guide groove is shorter in length), toobtain a favorable weld bead.

Shown below is a comparison between the embodiment of the presentinvention and the prior art.

The 12mm thick sample steel plates shown in the following Table 1 coatedwith a 20μthick wash primer, and they were butted together in a T-shapeas shown in FIGS. 3 and 4 to be used as the test pieces for welding.

                  Table 1                                                         ______________________________________                                        Chemical composition of sample steel plates                                   C         Si        Mn        p       S                                       ______________________________________                                        0.15      0.02      0.47      0.021   0.020                                   ______________________________________                                    

For welding, the submerged arc welding and the carbon dioxide gas arcwelding techniques were employed, and the chemical composition of theflux for submerged arc welding are respectively shown in Table 2 andTable 3.

                  Table 2                                                         ______________________________________                                        Chemical composition of welding wires                                                         C     Si      Mn      Ti                                      ______________________________________                                        CO.sub.2 gas arc welding                                                                        0.08    0.73    1.42  0.17                                  Submerged arc welding                                                                           0.12    0.01    1.43  --                                    ______________________________________                                    

                  Table 3                                                         ______________________________________                                        Chemical composition of flux for submerged                                    arc welding                                                                   SiO.sub.2                                                                             CaO     MgO     CaF.sub.2                                                                           MnO   Al.sub.2 O.sub.3                                                                     TiO.sub.2                          ______________________________________                                        40      20      20      6     6     4      4                                  ______________________________________                                    

The carbon dioxide gas as shielding gas is for welding, and the flowrate is 25/min.

Seven types of driving wire feed rolls (outer diameter 32mm) wereprepared as shown in Table 4. The A of Table 4 shows the wire feed rollused as the prior art, and the remainder is for the welding apparatuswith the feed roll according to the present invention.

                  Table 4                                                         ______________________________________                                        Wire feed rolls                                                                          Diameter of welding                                                                          Welding wire feed                                   Number of  wire used (mm) time ratio                                               grooves   For       For    For     For                                        in the    horizontal                                                                              vertical                                                                             horizontal                                                                            vertical                              No.  roll      plate     plate  plate   plate                                 ______________________________________                                        A    1         1.6       --     1       0                                     B    2         1.6       1.6    1       1                                     C    2         1.6       1.6    2       1                                     D    2         1.6       1.6    3       1                                     E    2         1.6       1.2    2       1                                     F    2         1.6       1.2    2       1                                     G    2         1.6       1.2    3       1                                     ______________________________________                                    

The speed of the feed rolls was set to 50 rpm.

Table 5 shows the welding conditions and results for and by thehorizontal fillet welding of the above-mentioned welding test pieces.

                  Table 5                                                         ______________________________________                                        ______________________________________                                        Embodiment (welding conditions and results)                                               Wire       Wire       welding cur-                                       Wire diameter   feed time  rent (amp)                                         feed used (mm)  ratio      **                                               Weld-   roll   For   For  For   For  For   For                           Test ing     (ta-   hori- ver- hori- ver- hori- ver-                          No.  method  ble    zontal                                                                              tical                                                                              zontal                                                                              tical                                                                              zontal                                                                              tical                         ***  *       4)     plate plate                                                                              plate plate                                                                              plate plate                         ______________________________________                                        1    SAW     A      1.6   --   1     0    300   --                            2    CO.sub.2                                                                              A      1.6   --   1     0    "     --                            3    "       B      1.6   1.6  1     1    "     300                           4    "       C      1.6   1.6  2     1    "     "                             5    "       D      1.6   1.6  3     1    "     "                             6    "       E      1.6   1.2  1     1    "     170                           7    "       F      1.6   1.2  2     1    "     "                             8    "       G      1.6   1.2  3     1    "     "                             9    SAW     F      1.6   1.2  2     1    "     "                             10   "       G      1.6   1.2  3     1    "     "                             Welding results                                                               Bead                                                                          appearance                                                                             Pits      Blowholes  Remarks                                         ______________________________________                                        Normal   Generated Generated                                                  Normal   Generated Generated  Prior art                                       Undercut Not       Not        Weld-  Method                                   caused   generated generated  ing    by the                                                                 wire   present                                  Normal   "         "          alter- inven-                                                                 nate   tion                                     Good     "         "          feed                                            Normal   "         "                                                          Good     "         "                                                          Good     "         A little                                                                      generated                                                  Good     "         Not                                                                           generated                                                  Good     "         "                                                          ______________________________________                                         *CO.sub.2 : Carbon dioxide gas arc welding SAW: Submerged arc welding         **Arc voltage: 30V for 300 apm 26V for 170 amp                                ***Welding speed: 70cm.min.                                              

As can be seen from the above Table, according to the prior processes inwhich the steel plate coated with a wash primer is used, the pits areobserved on the surface of the weld heads. According to the method ofthe present invention on the other hand, no pits are observed on theweld bead surface, though some blowholes are generated.

It was also found that with the wire feed conditions of the presentinvention, to obtain good bead appearance free from the generation of anundercut, it was necessary to make the wire diameter for the verticalsteel plate side smaller than that for the horizontal steel plate sideand/or to make the wire feed time for the vertical steel plate sidesmaller than that for the horizontal steel plate side.

Thus, in the horizontal fillet welding of the steel plate coated with ananti-rust paint, the prior art renders the welding difficult to automatebecause of the generation of blowholes. However, according to thepresent invention generation of blowholes is avoided, and while onewelding wire is ignited, the other welding wire which is extinguished ispositioned apart from the welding zone so that it is unnecessary toinsulate these two welding wires from each other. Therefore, thehorizontal fillet welding technique is capable of being automated inaccordance with the invention.

Furthermore, the method according to the present invention can be usedas a preceding head with the conventional method used as a followinghead to produce the same effect, and it can be applied not only to steelplates but to other steel materials as well.

What is claimed is:
 1. An apparatus for horizontal fillet weldingtogether a vertical steel plate and a horizontal steel plate buttedtogether in a T-shape and having a line of intersection, comprising apair of welding wires, means for alternately feeding said wires atdifferent rates of feed, a power supply nozzle through which said wiresare fed, said power supply nozzle being directed toward said line ofintersection and so disposed that one of said wires is fed to saidvertical plate and the other of said wires is alternately fed to saidhorizontal plate, a welding power source connected to said nozzle and toone of said plate for passing an electric current alternately throughsaid wires for the fillet welding of said plates, means for moving saidnozzle along said line of intersection; and wherein said feed meanscomprises a feed roll rotatable at a constant speed, said roll having apair of parallel guide grooves around on the outer peripheral surfacethereof, guide grooves respectively receiving said welding wires, and apressure roll in rotating contact with said outer surface of said driveroll; each of said guide grooves consisting of a narrow portion and awide portion, said narrow portion of each guide groove having asectional dimension substantially equal to the diameter of each weldingwire and serving to feed each welding wire to said power supply nozzlewhen said presure roll is in contact with said narrow portion so as toengage each welding wire with said pressure roll, said wide portion ofeach guide grooves having a sectional dimension greater than thediameter of each welding wire and serving to stop the feeding of eachwelding wire to said power supply nozzle by separating each welding wirefrom the surface of said pressure roll when said wide portion is incontact with said pressure roll, said narrow and wide portions being sodisposed relative to one another that when one of said guide grooves forthe welding wire to be fed to said vertical steel plate is in contact atits narrow portion with said pressure roll, another of said guidegrooves for the welding wire to be fed to the horizontal steel plate isin contact at its wide portion with said pressure roll, and when saidone guide groove is in contact at its wide portion with said pressureroll, said another guide groove is in contact at its narrow portion withsaid pressure roll; and the ratio of the length of said narrow portionto said wide portion of the guide groove for said welding wire to be fedto said vertical steel plate is in a range of 1:1 to 1:4, whereby saidwelding wires are fed alternately to said vertical steel plate and tosaid horizontal steel plate in a proportion of the ratio of 1:1 to 1:4.2. Apparatus as set forth in claim 1, wherein the ratio of the wire tobe fed to said vertical plate to the wire to be fed to the horizontalplate is, in diameter, in the range of 1:1 to 3:4.